Detecting the drift of the data valid window in a transaction

ABSTRACT

Disclosed herein are system, apparatus, article of manufacture, method and/or computer program product embodiments for detecting the drift of the data valid window in a transaction. An embodiment operates by configuring a data capture range comprising data capture points, measuring values of a signal at the data capture points, and detecting the drift of the data valid window based on the values at the data capture points.

BACKGROUND

Generally, in synchronous serial communications, transmitted andreceived bits are synchronized to a common clock signal. When data istransferred between a transmitter and a receiver, a data valid windowwide enough and occurring at a predictable time is used in order toensure proper data capture by the receiver. The timing of the data validwindow depends on the round-trip delay of the clock and data. Thisround-trip delay depends on the process, temperature, operating voltageconditions, and of the printed circuit board (PCB) layout. Although theprocess and PCB layout are stable, the temperature and operating voltagecan vary over time. For example, the variation of the operating voltagehas a much shorter time constant than that of the temperature.

One method for predicting the timing of the data valid window is a datalearning pattern, such as the preamble pattern disclosed by U.S. Pat.No. 8,417,874, which is hereby incorporated herein by reference in itsentirety. Using DLP, the transmitter sends a pre-determined datalearning pattern at the beginning of each data frame. For each dataline, the receiver can calibrate the data capture point so that it is inthe center of the data valid window. However, for long data frames,there is the possibility that the timing of the data valid window driftsdue to changes in the operating conditions, e.g. the operation voltage.In some cases, this drift may lead to a situation where the data cannotbe reliably captured anymore, causing corruption of received data. Evenwith the use of DLP, the data corruption may not be detected within thedata frame.

SUMMARY

Provided herein are system, apparatus, article of manufacture, methodand/or computer program product embodiments, and/or combinations andsub-combinations thereof, for detecting the drift of the data validwindow in a transaction.

An embodiment includes a computer implemented method for detecting thedrift of the data valid window in a transaction. The method operates byconfiguring a data capture range comprising data capture points,measuring values of a signal at the data capture points, and detectingthe drift of the data valid window based on the values at the datacapture points.

Another embodiment includes a system for detecting the drift of the datavalid window in a transaction. The apparatus includes a memory and atleast one processor coupled to the memory. The processor is configuredto configure a data capture range comprising data capture points,measure values of a signal at the data capture points, and detect driftof the data valid window based on the values at the data capture points.

A further embodiment includes a tangible computer-readable device havinginstructions stored thereon that, when executed by at least onecomputing device, cause the computing device to perform operations. Theoperations include configuring a data capture range comprising datacapture points, measuring values of a signal at the data capture points,and detecting drift of the data valid window based on the values at thedata capture points.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated herein and form a part of thespecification.

FIG. 1 is a block diagram of a system for detecting the drift of thedata valid window in a transaction, according to an example embodiment.

FIG. 2 is a flowchart illustrating a process for detecting the drift ofthe data valid window in a transaction, according to an exampleembodiment.

FIG. 3 is a block diagram of signals being processed using a process fordetecting the drift of the data valid window in a transaction, accordingto an example embodiment.

FIG. 4 is a block diagram of a circuit for detecting the drift of thedata valid window in a transaction, according to an example embodiment.

FIG. 5 is an example computer system useful for implementing variousembodiments.

In the drawings, like reference numbers generally indicate identical orsimilar elements. Additionally, generally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example system 100 that includes amaster device 102, a slave device 104, a clock bus 106, a master out,slave in (MOSI) bus 108, and a master in, slave out (MISO) bus 110.Master device 102 or slave device 104 can be a processor,microcontroller (MCU) an integrated circuit, application-specificintegrated circuit (ASIC), field-programmable gate array (FPGA),processing core, or any combination thereof. Although system 100 isdepicted as having one master device, one slave device, and three buses,embodiments of the invention support any number of master devices, slavedevices, and buses. For example, system 100 could have two buses, inwhich one is a clock bus and the other is a MISO or MOSI bus.

In an embodiment, master device 102 transmits a clock signal over clockbus 106 to slave device 104. Both master device 102 and slave device 104use clock signal for synchronous, serial communication over one or morebuses, e.g. MOSI bus 108 and MISO bus 110.

In an embodiment, master device 102, acting as the transmitter,transmits a data signal to slave device 104 over MOSI bus 108. Slavedevice 104 derives information from the data signal using, in part, theclock signal received from master device 102.

In an embodiment, master device 102, acting as the receiver, receives adata signal from slave device 104, acting as the transmitter, over MISObus 110. Master device 102 derives information from the data signalusing, in part, the clock signal it sent to slave device 104 over clockbus 106.

In an embodiment, master device 102 has one or more slave select buses(not shown) that connect to one or more slave devices, such as slavedevice 104. Master device 102 can transmit a signal over one of slaveselect buses to select the active stave device.

The data signal received by a receiver can experience distortion of thedata signal's phase or frequency. The distortion can change over time,such as distortion caused by variation of design or operatingconditions. As a result, the data valid window of the signal may driftand fall out of sync with the clock signal. In an embodiment, thereceiver detects the drift of the data valid window in a transaction.For example, master device 102 can detect drift of the data valid windowin a data signal received over MISO 110, or slave device 104 can detectdrift of the data valid window in a data signal received over MOSI 108.Although master device 102 is the receiver in various of the followingexamples, embodiments of the invention support slave device 104 beingthe receiver.

Detecting drift of the data valid window in serial communications hasnumerous uses. For example, and without limitation, drift of the datavalid window can be detected in communications between one or morememory controllers and one or more MCUs, one or more memory controllersand one or more other devices, or in communications between receiversand transmitters of synchronous serial protocols, in general.

FIG. 2 is a flowchart illustrating a process 200 for detecting drift ofthe data valid window in a transaction, according to an exampleembodiment. Process 200 can be performed by processing logic that cancomprise hardware (e.g., circuitry, dedicated logic, programmable logic,microcode, etc.), software (e.g., instructions run on a processingdevice), or a combination thereof. For example, process 200 may beperformed by master device 102 or slave device 104.

In block 202, a signal is received. In an embodiment, master device 102receives the signal from slave device 104 over MISO 110.

In block 204, a data capture range (DCR) comprising data capture pointsis configured to fall within the data valid window (DVW). In anembodiment, master device 102 configures the data capture range.

A DCR refers to a time period during which a value from the signal isread. In an embodiment, to capture the data reliably, the DCR is smallerthan and positioned within the DVW. The DCR can be configured tocorrespond to regular events provided by a clock signal, such as a clocksignal sent over clock bus 106. For example, for a clock signal having acycle time t, a DCR can be configured to have a width of time t/2, and aseries of DCRs can be configured to begin at ¼ t after the beginning ofeach cycle and end at ¼ t before the end of the cycle, respectively.Although this example of a DCR will be used for purposes ofillustration, embodiments of the invention support DCRs with variouswidths and positions.

In an embodiment, the DCR is set based on a data learning pattern (DLP).A DLP may refer to a particular signal sent by the transmitter to thereceiver. Because the characteristics of the DLP are known to thereceiver, the receiver can synchronize an incoming signal to the clockbased on the DLP. However, embodiments of the invention support othertechniques for synchronizing an incoming signal to the clock, such usinga fixed data pattern read from a particular address.

A DCR comprises data capture points (DCP). A DCP refers to a point intime within the DCR at which data from the signal is read. In anembodiment, the DCR has three DCPs—a left DCP, a center DCP, and a rightDCP. The center DCP may occur at the center of the DCR. The left DCP mayoccur at the beginning of the DCR, and the right DCP may occur at theend of the DCR. Although these example DCPs will be used for purposes ofillustration, embodiments of the invention support DCRs with any numberof DCPs, and the DCPs can be configured to occur at any times within theDCR. For example, a DCR may have two DCPs defining the start and the endof the DCR. The DCR itself can be arbitrarily located within a DVW. Asanother example, a DCR may have eight DCPs that are spaced at equal timeintervals within the DCR. Similarly, although the term “center” is usedwhen referring to the center DCP, the center DCP is not limited tooccurring only at the center of the DCR, and other embodiments of theinvention support a DCR having a center DCP that occurs at any otherpoint other than the center of the DCR. Any one of the values measuredat the DCPs can be used as the value of the signal during the DVW. Forexample, the value measured at center DCP can be used as the value ofthe signal during the DVW.

The size and arrangement of the DCR within a DVW can impact thesensitivity of the receiver to detecting drift. For example, if the DCRis rather small compared to the DVW so that the DCPs are placed closertogether and farther from the edges of the DVW, the DVW may not detectdrift as readily as other configurations. This can result in atransaction experiencing drift being able to continue longer, but canalso result in being less sensitive to drift of the DVW. In anotherexample, when the DCR is getting near to the size of the DVW so that theDCPs are placed farther apart and closer to the edges of the DVW, theDCR can detect a drift of the DVW more readily than otherconfigurations. This can result in more frequent detections, which canimprove sensitivity but can result in more frequent reconfigurations ofthe DCR or restarting of the transaction.

In block 206, values of the signal at the DCPs are measured. In anembodiment, master device 102 measures the values of the signal at theDCPs. Measuring the values can include determining whether the signalrepresents a high or low value, a logical 1 or 0, or any one of a rangeof values. The values may be measured by detecting levels of voltage,current, or any combination thereof. A measured value may be the same atdifferent DCPs even though the signal is not identical at the differentDCPs. For example, the measured values at two DCPs may both be a logical1 even though the voltages measured at those DCPs vary, e.g. 2.4 V and2.3 V.

In block 208, drift of the DVW is detected based on the value of theDCPs. In an embodiment, master device 102 detects the drift of thesignal.

In an embodiment, master device 102 detects drift of the DVW with a DCRhaving two DCPs when the values measured at two DCPs differ. Forexample, within the DCR, the value at a first DCP may be measured as a1, and the value at a second DCP may be measured as a 0. Because themeasured values differ, drift of the DVW is detected, and consequently,the points within the DCR cannot all be reliably measured to have thesame value.

In an embodiment, master device 102 detects drift of the DVW with a DCRhaving three DCPs (e.g. left DCP, center DCP, and right DCP) when thevalue measured at the left DCP differs from the values measured at theother DCPs (in case of drift of the DVW to the right) or the valuemeasured at the right DCP differs from the values measured at the otherDCPs (in case of drift of the DVW to the left). For example, the valuemeasured at the left DCP may be measured as a 1, and the values measuredat the center and right DCPs may be measured as a 0. Because themeasured values differ, drift of the DVW is detected, and consequently,the points within the DCR cannot all be reliably measured to have thesame value. As another example, the center DCP value may be measured asa 1, but the left and right DCP values may be measured a 0. As in theprevious example the points within the DCR are not all reliably measuredto have the same value. But because the measured values differ in morethan one neighbored pair of DCPs, data corruption is detected. The datacorruption may be caused due to drift (e.g drift unrecognized over anunchanging series of 1's or 0's) or some other cause of disturbance notexplained by drift alone. In this case the transaction must be restartedat the point where the corruption has been detected.

In an embodiment, when values are measured at three or more DCPs withina DCR, the direction of the drift can be detected. For example,referring back to the three-DCP example, a value measured at the leftDCP may differ from a same value measured at the center and right DCPs.From this information, it can be inferred that not only has drift of theDVW occurred, but also that the DVW has drifted past the DCR, and thatthe DCR could be shifted to later in time to correct for the drift. Asanother example, a value measured at the right DCP may differ from asame value measured at the center and left DCPs. From this information,it can be inferred that not only has drift of the DVW occurred, but alsothat the DVW has drifted in front of the DCR, and that the DCR could beshifted to earlier in time to correct for the drift. Although detectionof the direction of the drift has been discussed using three DCPs in aDCR, embodiments of the invention support detecting the direction of thedrift with four or more DCPs using similar techniques, e.g. finding oneor more differing values near the boundaries of the DCR. When thedirection of the drift is correctly identified, the transaction cancontinue without needing to restart the transaction.

In an embodiment, drift of the DVW may occur but be initiallyunrecognized when more than one of the same values are transmittedsequentially. For example, drift of the DVW may occur duringtransmission of a series of 1's (e.g. “111111”), but the drift may notbe detected when it occurs because measurement of values at varying DCPswill have the same values, even if the DCPs are measuring values thatare outside the DVW. As long there is no signal transition, no error isproduced when capturing data at a wrong position. After a long series ofsame values, the ability might get lost to determine the direction ofthe drift, because the drift already might have accumulated to affectthe majority of the DCPs. For example, in case the DVW has moved by awhole clock period t, the drift would not be detected. In such cases thedata is retransmitted to ensure the integrity of the received data. Toobserve the time limit for data transfers of the same value withouttransition, a counter can be implemented that tracks the number of timesthe same measured value occurs in a series of DCRs. Depending on theexpected maximum change of the position of the DVW per time, a limit forthis counter can be defined. In case the limit is exceeded, dataintegrity may not be able to be ensured anymore. To ensure dataintegrity, data can be retransmitted, starting from the point before thelimit has been detected.

In block 210, the DCR is reconfigured in response to detecting the driftof the DVW. In an embodiment, master device 102 reconfigures the DCR.The DCR can be reconfigured in various ways.

In an embodiment, the position of the DCR is adjusted relative to aclock signal during the transaction by adjusting each individual DCPbelonging to the DCR. In an embodiment, master device 102 adjusts theDCR. For example, the position of the DCR is adjusted so that the DCR,and consequently the DCPs, samples the signal later in time. As anotherexample, the DCR is adjusted so that the DCR, and consequently the DCPs,samples the signal earlier in time. The DCR can be shifted by apredetermined amount, e.g. ¼ t, or any other amount. Alternatively oradditionally, the size of the DCR can be adjusted, i.e. made longer orshorter.

In an embodiment, the position of the DCR is adjusted during atransaction. When this happens, the transaction can continue withoutincurring the overhead associated with restarting the transaction andbeginning to send a new frame, which can include, for example, resettingthe DCR based on a DLP.

In an embodiment, the position of the DCR is determined based on thevalues at the DCPs. In an embodiment, master device 102 determines theposition. As discussed above, the values captured at the DCPs, and theidentities of the DCPs that have differing values than the others, caninform master device 102 of the direction of the drift of the DVW, andtherefore the direction to shift the DCR to compensate for the detecteddrift.

In an embodiment, the DCR is reconfigured after restarting thetransaction. In an embodiment, master 102 reconfigures the DCR. Forexample, when the drift is detected, master device 102 can stop thecurrent transaction with slave device 104. The transaction can berestarted whether the direction of the drift is known or not. Forexample, referring back to the three-DCP example, the value of thesignal measured at the center DCP can differ from the same valuemeasured at the left and right DCPs, and the direction of the drift maynot be ascertained, even though a distortion has been detected. Becausethe integrity of the signal in the DVW is in question, the transactionmay be restarted. Data values prior to the detection of the datacorruption can be retained, so that the transaction is restarted at thepoint when the data integrity is in question. When the transactionrestarts, the DCR can be reconfigured in one or more of various ways,e.g. using a DLP.

FIG. 3 is a block diagram of signals being processed using a process fordetecting the drift of the DVW in a transaction and includes signals302, 304, 306, 308, and 310. In this example, signal 302 is a signalreceived by master device 102 from slave device 104, and is unaffectedby operating conditions. Signals 304, 306, 308, and 310 are signals thatcarry the same information as signal 302 (i.e. “0101010”), but havebecome distorted during transmission due to one or more operatingconditions. In this example, the DCR is ½ t wide, and begins ¼ t afterthe beginning of every clock cycle, e.g. t₁+¼ t, t₂+¼ t, etc. The dotson each of the signals represent DCPs within the DCRs.

In signal 302, which does not exhibit drift of the DVW, each valuemeasured in the series of DCRs is correct. Hence, when the signal ismeasured at a DCP in the center of the DCR, as indicated by the dots onthe signal, the values will result in “0101010”.

Signals 304 and 306 exhibit drift of the DVW, so the values measuredduring the DCR may be incorrect. For example, if the DCP is the centerof the DCR, the value of signals 304 and 306 will both be incorrectlyreceived as “0101101”.

Signal 308 depicts how the drift of the DVW is detected in a transactionby employing an embodiment of the invention. In this embodiment, the DCRcomprises 3 DCPs: a left DCP at 0, a center DCP at ¼ t, and a right DCPat ½ t of the DCR. Further, the value of the signal is that measured atthe center DCP. The DCRs are depicted as boxes surrounding the DCP dots.

In the first and second DCRs, which occur between times t₁+¼ t and t₁+¾t and times t₂+¼ t and t₂+¾ t, respectively, the values measured at allthree DCPs are the same, so the values can be relied upon. In the thirdDCR, which occurs between times t₃+¼ t and t₃+¾ t, the value of thesignal at the left DCP differs from those of the signal at the centerand right DCPs. This discrepancy indicates that drift of the DVW hasoccurred, and that the DCR should be shifted later in time. Thus, DCRcan be shifted ¼ t later in time, so that the fourth DCR starts at timet₄+½ t. In the fourth DCR, the values measured at all three DCPs are thesame, so the values can be relied upon. In the fifth DCR, which occursbetween times t₅+½ t and t₆+½ t, the value of the signal at the left DCPdiffers from those of the signal at the center and right DCPs. Thisdiscrepancy indicates that drift of the DVW has occurred, and that theDCR should be shifted later in time. Thus, DCR can be shifted ¼ t laterin time, so that the sixth DCR starts at time t₆+¾ t. In the sixth DCRthe value of the signal at the left DCP differs from those of the signalat the center and right DCPs. This discrepancy indicates that drift ofthe DVW has occurred, and that the DCR should be shifted later in time.Thus, DCR can be shifted ¼ t later in time, so that the seventh DCR (notshown) starts at time t₇+t. After undergoing this process, each of thevalues measured at the center DCPs correctly correspond to thetransmitted “0101010”.

Signal 310 depicts how an example DVW drift is detected in a transactionby employing an embodiment of the invention. In this embodiment, the DCRcomprises 3 DCPs: a left DCP at 0, a center DCP at ¼ t, and a right DCPat ½ t. Further, the value of the signal is that measured at the centerDCP. The DCRs are depicted as boxes surrounding the DCP dots.

In the first and second DCRs, which occur between times t₁+¼ t and t₁+¼t and times t₂+¼ t and t₂+¾ t, respectively, the values measured at allthree DCPs are the same, so the values can be relied upon. In the thirdDCR, which occurs between times t₃+¼ t and t₃+¾ t, the value of thesignal at the left DCP differs from those of the signal at the centerand right DCPs. This discrepancy indicates that drift of the DVW hasoccurred, and in this embodiment, the transaction is restarted upondetecting the drift. The DCR is reset using a DLP. In the remainingDCRs, the values measured at all the three DCPs in each DCR are thesame, so the values can be relied upon. After undergoing this process,each of the values measured at the center DCPs correctly correspond tothe transmitted “0101010”.

FIG. 4 is a block diagram of a circuit 400 that includes serial datainput (SDI) 402, bit rate clock (BRC) 404, sampling clock generator andselector 406, DCP configuration registers 408, left flip-flop (FF) 410,center FF 412, right FF 414, synchronizer 416, gates 418 and 420, leftsampling error 422, right sampling error 424, and received data 426.

In an embodiment, master device 102 comprises circuit 400. SDI 402 isreceived over MISO 106, and BRC 404 is that transmitted on clock bus106.

In an embodiment, sampling clock generator and selector 406 uses BRC 404and DCP configuration information from DCP configuration registers 408to signal to FFs 410, 412, and 414 to sample and store the value fromSDI 402. For example, the DCPs can be at times ¼ t, ½ t, and ¾ t.Sampling clock generator and selector 406 reads the DCP configurationfrom DCP configuration registers 408. When the cycle of BRC 404 reachestime ¼ t, sampling clock generator and selector 406 will signal to leftFF 410 to read and store the current value of SDI 402. When the cycle ofBRC 404 reaches time ½ t, sampling clock generator and selector 406 willsignal to center FF 412 to read and store the current value of SDI 402.When the cycle of BRC 404 reaches time ¾ t, sampling clock generator andselector 406 will signal to right FF 414 to read and store the currentvalue of SDI 402.

In an embodiment, DCP configuration registers 408 comprise threeregisters, one for each of the left, right, and center sampling point.Each register can be configured to a value, e.g. a value between 0 and23. Configuration of a register to the value n has the consequence ofdelaying the corresponding sampling clock by n delay buffers, units, ortaps. In some cases, the delay is n*delay tap, wherein delay tap is thenominal delay of one delay buffer. Often, delay tap depends on theprocess, voltage, temperature conditions, so the real delay value can beapproximated by the formula above. Because the goal is to sample thedata in the center, and not necessarily to configure a delay with anexact delay time, some iterations can be used to correctly configure thesampling delay. Configuring the sampling delay can be accomplished, e.g.by using different delay values and checking the correctness of the DLP.Although this example configuration is discussed, embodiments of theinvention support other implementations for setting the DCPconfiguration, e.g. using a delay-locked loop (DLL) for generating a setof delayed clocks with the same frequency, by using a much higher inputfrequency and different edges for sampling, or by delaying the data by anumber of delay buffers (for example m-n delay buffers, where m is thetotal number of available delay buffers) and capturing the data one ormore sampling clock cycles later.

In an embodiment, synchronizer 416 outputs the results from FFs 410,412, and 414 at or during a set time. For example, synchronizer canoutput the results independent from the phase of the DCPs, synchronousto the BRC 404.

In an embodiment, gates 418 and 420 compare the values at the left andright DCPs, respectively, to the value at the center DCP. Gate 418outputs sampling error 422 when the value at the left DCP is not thesame as the value at the center DCP. Similarly, gate 420 outputssampling error 424 when the value at the right DCP is not the same asthe value at the center DCP.

In an embodiment, received data 426 is the value measured at the centerDCP. Received data 426 can be used as the value of the signal during theDCR, even if drift is detected and a left sampling error 422 or rightsampling error 424 is outputted. If both left and right sampling errors422 and 424 are detected, that suggests that received data 426 may be aninvalid or unreliable measurement of the signal in the DCR.

Example Computer System

Various embodiments can be implemented, for example, using one or morewell-known computer systems, such as computer system 500 shown in FIG.5. Computer system 500 can be any well-known computer capable ofperforming the functions described herein, such as computers availablefrom International Business Machines, Apple, Sun, HP, Dell, Sony,Toshiba, etc. Embodiments of the invention (or portions thereof) canalso be implemented using hardware state machines, application-specificintegrated circuits (ASIC) and/or other hardware components specificallyconfigured to perform the operations described herein.

Computer system 500 includes one or more processors (also called centralprocessing units, or CPUs), such as a processor 504. Processor 504 isconnected to a communication infrastructure or bus 506.

One or more processors 504 may each be a graphics processing unit (GPU).In an embodiment, a GPU is a processor that is a specialized electroniccircuit designed to rapidly process mathematically intensiveapplications on electronic devices. The GPU may have a highly parallelstructure that is efficient for parallel processing of large blocks ofdata, such as mathematically intensive data common to computer graphicsapplications, images and videos.

One or more processor 504 may each be a hardware state machine, ASIC, orcontroller.

Computer system 500 also includes user input/output device(s) 503, suchas monitors, keyboards, pointing devices, etc., which communicate withcommunication infrastructure 506 through user input/output interface(s)502.

Computer system 500 also includes a main or primary memory 508, such asrandom access memory (RAM). Main memory 508 may include one or morelevels of cache. Main memory 508 has stored therein control logic (i.e.,computer software) and/or data.

Computer system 500 may also include one or more secondary storagedevices or memory 510. Secondary memory 510 may include, for example, ahard disk drive 512 and/or a removable storage device or drive 514.Removable storage drive 514 may be a floppy disk drive, a magnetic tapedrive, a compact disk drive, an optical storage device, tape backupdevice, and/or any other storage device/drive.

Removable storage drive 514 may interact with a removable storage unit518. Removable storage unit 518 includes a computer usable or readablestorage device raving stored thereon computer software (control logic)and/or data. Removable storage unit 518 may be a floppy disk, magnetictape, compact disk, DVD, optical storage disk, and/any other computerdata storage device. Removable storage drive 514 leads from and/orwrites to removable storage unit 518 in a well-known manner.

According to an exemplary embodiment, secondary memory 510 may includeother means, instrumentalities or other approaches for allowing computerprograms and/or other instructions and/or data to be accessed bycomputer system 500. Such means, instrumentalities or other approachesmay include, for example, a removable storage unit 522 and an interface520. Examples of the removable storage unit 522 and the interface 520may include a program cartridge and cartridge interface (such as thatfound in video game devices), a removable memory chip (such as an EPROMor PROM) and associated socket, a memory stick and USB port, a memorycard and associated memory card slot, and/or any other removable storageunit and associated interface.

Computer system 500 may further include a communication or networkinterface 524. Communication interface 524 enables computer system 500to communicate and interact with any combination of remote devices,remote networks, remote entities, etc. (individually and collectivelyreferenced by reference number 528). For example, communicationinterface 524 may allow computer system 500 to communicate with remotedevices 528 over communications path 526, which may be wired and/orwireless, and which may include any combination of LANs, WANs, theInternet, etc. Control logic and/or data may be transmitted to and fromcomputer system 500 via communication path 526.

In an embodiment, a tangible apparatus or article of manufacturecomprising a tangible computer useable or readable medium having controllogic (software) stored thereon is also referred to herein as a computerprogram product or program storage device. This includes, but is notlimited to, computer system 500, main memory 508, secondary memory 510,and removable storage units 518 and 522, as well as tangible articles ofmanufacture embodying any combination of the foregoing. Such controllogic, when executed by one or more data processing devices (such ascomputer system 500), causes such data processing devices to operate asdescribed herein.

Based on the teachings contained in this disclosure, it will be apparentto persons skilled in the relevant art(s) how to make and use theinvention using data processing devices, computer systems and/orcomputer architectures other than that shown in FIG. 5. In particular,embodiments may operate with software, hardware, and/or operating systemimplementations other than those described herein.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the invention as contemplated bythe inventors, and thus, are not intended to limit the invention or theappended claims in any way.

While the invention has been described herein with reference toexemplary embodiments for exemplary fields and applications, it shouldbe understood that the invention is not limited thereto. Otherembodiments and modifications thereto are possible, and are within thescope and spirit of the invention. For example, and without limiting thegenerality of this paragraph, embodiments are not limited to thesoftware, hardware, firmware, and/or entities illustrated in the figuresand/or described herein. Further, embodiments (whether or not explicitlydescribed herein) have significant utility to fields and applicationsbeyond the examples described herein.

Embodiments have been described herein with the aid of functionalbuilding blocks illustrating the implementation of specified functionsand relationships thereof. The boundaries of these functional buildingblocks have been arbitrarily defined herein for the convenience of thedescription. Alternate boundaries can be defined as long as thespecified functions and relationships (or equivalents thereof) areappropriately performed. Also, alternative embodiments may performfunctional blocks, steps, operations, methods, etc. using orderingsdifferent than those described herein.

References herein to “one embodiment,” “an embodiment,” “an exampleembodiment,” or similar phrases, indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it would be within the knowledge of persons skilled in therelevant art(s) to incorporate such feature, structure, orcharacteristic into other embodiments whether or not explicitlymentioned or described herein.

The breadth and scope of the invention should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed is:
 1. A method for detecting drift of a data validwindow in a transaction, comprising: configuring a data capture rangecomprising data capture points; measuring values of a signal at the datacapture points; and detecting the drift of the data valid window basedon the values at the data capture points.
 2. The method of claim 1,further comprising: reconfiguring the data capture range in response todetecting the drift.
 3. The method of claim 2, the reconfiguring furthercomprising: adjusting the position of the data capture range relative toa clock signal during the transaction.
 4. The method of claim 3, theadjusting further comprising: determining the position based on thevalues at the data capture points.
 5. The method of claim 2, thereconfiguring further comprising: reconfiguring the data capture rangeafter stopping and before restarting the transaction.
 6. The method ofclaim 1, the configuring further comprising: setting the data capturerange based on a data learning pattern.
 7. The method of claim 1,wherein the data capture points comprise at least a left data capturepoint, a right data capture point, and an interior data capture pointbetween the left and right data capture points, and further comprising:determining that a value at the interior data capture point isunreliable when a first sampling error is detected at the right datacapture point and a second sampling error is detected at the left datacapture point; or determining that the value at the interior datacapture point is reliable when no sampling error is detected at theright data capture point or no sampling error is detected at the leftdata capture point.
 8. A system, comprising: a memory; and at least oneprocessor coupled to the memory and configured to: configure a datacapture range comprising data capture points; measure values of a signalat the data capture points; and detect drift of a data valid windowbased on the values at the data capture points.
 9. The system of claim8, the at least one processor further configured to: reconfigure thedata capture range in response to detecting the drift.
 10. The system ofclaim 9, wherein to reconfigure, the at least one processor isconfigured to: adjust the position of the data capture range relative toa clock signal during the transaction.
 11. The system of claim 10,wherein to adjust, the at least one processor is configured to:determine the position based on the values at the data capture points.12. The system of claim 9, wherein to reconfigure, the at least oneprocessor is configured to: reconfigure the data capture range afterstopping and before restarting the transaction.
 13. The system of claim8, wherein to configure, the at least one processor is configured to:set the data capture range based on a data learning pattern.
 14. Thesystem of claim 8, wherein the data capture points comprise at least aleft data capture point, a right data capture point, and an interiordata capture point between the left and right data capture points, andwherein the at least one processor is configured to: determine that avalue at the interior data capture point is unreliable when a firstsampling error is detected at the right data capture point and a secondsampling error is detected at the left data capture point; or determinethat the value at the interior data capture point is reliable when nosampling error is detected at the right data capture point or nosampling error is detected at the left data capture point.
 15. Atangible computer-readable device having instructions stored thereonthat, when executed by at least one computing device, causes the atleast one computing device to perform operations comprising: configuringa data capture range comprising data capture points; measuring values ofa signal at the data capture points; and detecting drift of a data validwindow based on the values at the data capture points.
 16. Thecomputer-readable device of claim 15, the operations further comprising:reconfiguring the data capture range in response to detecting the drift.17. The computer-readable device of claim 16, the reconfiguringcomprising: adjusting the position of the data capture range relative toa clock signal during the transaction.
 18. The computer-readable deviceof claim 17, the adjusting comprising: determining the position based onthe values at the data capture points.
 19. The computer-readable deviceof claim 16, the reconfiguring comprising: reconfiguring the datacapture range after stopping and before restarting the transaction. 20.The computer-readable device of claim 15, the configuring comprising:setting the data capture range based on a data learning pattern.
 21. Thecomputer-readable device of claim 15, wherein the data capture pointscomprise at least a left data capture point, a right data capture point,and an interior data capture point between the left and right datacapture points, and the operations further comprising: determining thata value at the interior data capture point is unreliable when a firstsampling error is detected at the right data capture point and a secondsampling error is detected at the left data capture point; ordetermining that the value at the interior data capture point isreliable when no sampling error is detected at the right data capturepoint or no sampling error is detected at the left data capture point.